HAYWARD, JAMES L.* AND DENNIS W. WOODLAND. Biology Department, Andrews University, Berrien Springs, MI 49104-0410. - Plant diversity and ecology of Protection Island, Washington.
Protection Island, Washington, is located at the southeast end of the
Strait of Juan de Fuca in the rain shadow of the Olympic Mountains
(approximate rainfall=41 cm/year). The 160-hectare island contains one
of the largest breeding colonies of seabirds and harbor seals
(Phoca vitulina) in the Pacific Northwest. In 1988 most of the
island was designated as the Protection Island National Wildlife
Refuge. While Protection Island’s habitat structure has changed little
since George Vancouver's 1792 description of the island, published
information on its flora consists only of incidental remarks appended
to faunal studies. As part of a long-term assessment of Protection
Island’s biodiversity, vascular plants were collected from 1997-2000.
During June-August 1999, plant diversity and density were sampled in
311 randomly-selected, 1 x 1-m quadrats along 15 transects. Introduced
species accounted for 42% of the 106 species collected overall, and
for 55% of 20 species of grasses. Exotics accounted for most of the
grassland cover. Field bindweed (Convolvulus arvensis) and
Canada thistle (Cirsium arvense) were particularly invasive.
Snowberry (Symphoricarpos albus) was common along north-facing
slopes. Two small forested areas, dominated by Douglas fir
(Pseudotsuga menziesii), were commonly bordered by Douglas
maple (Acer glabrum), Pacific madrone (Arbutus
menziesii), ocean spray (Holodiscus discolor), and Nootka
rose (Rosa nutkana). Weedy species dominated the
sparsely-vegetated nesting areas of rhinoceros auklets (Cerorhinca
monocerata) and glaucous-winged gulls (Larus glaucescens).
A vegetation map of the island was created using ground-truthed,
aerial photographs. A species-association matrix highlights
correlations among species distribution patterns. Results from this
study have raised questions about the impact of previous agricultural
practices, real estate development, and fire prevention on the
island’s grassland community. They have also led to hypotheses about
plant/nesting-bird interactions and about the value of controlled
burns of the island’s grassland areas. These hypotheses are currently
being tested.
Key words: diversity, flora, grassland, Protection Island WA, tall-grass prairie